Cream together butter and brown sugar. Mix in egg, water and vanilla. Make oat flour: Pulse the two cups of oats for grinding in a food processor for one minute, or until a flour-like texture. Stir together cinnamon, salt, baking soda, rolled oats and ground oats. In three increments, add the dry ingredients to the wet. Spoon out about two tablespoons of dough per cookie. Flatten each cookie onto a parchment-lined baking sheet. Bake at 350* for 15 minutes. They will crisp up as they cool. Cool completely before filling.